net, neigh: Fix null-ptr-deref in neightableclear()
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.14.299 by commit 0d38b4ca6679e72860ff8730e79bb99d0e9fa3b0, it was introduced in version v4.14.292 by commit 9bbaed571c4bf1b62ac8703cb359dc090efc3455. For more details please see the references link.